The burning of fossil fuels was long considered to be an environmentally friendly source of energy to produce heat and power. Atmospheric disposal of the carbon dioxide (CO2) formed in the combustion with air was a very convenient way to dispose of even large amounts (above 50 000 metric tons per day per lignite-fired power plant in some instances). Concerns about the negative effects of the greenhouse gas CO2 on the climate are driving research into CO2 capture and valorization. Considered thermodynamically, CO2 is at a very low level and therefore very difficult to reduce back into useful products.
In nature, CO2 is reduced to carbohydrates by photosynthesis. This process with its multiplicity of elementary steps at different times and at molecularly different places is very difficult to copy on a large industrial scale. Three possible ways a., b. and c. to reduce CO2 by means of sunlight may be discussed.
a. Photocatalysis is the most complex and difficult way. A catalyst is to convert CO2 in the presence of water directly into methane CH4 or methanol CH3OH.CO2+2H2O→CH4+2O2 CO2+2H2O→CH3OH+2O2 
These processes normally only proceed “willingly” in the opposite direction, as a combustion. A complex logistics of materials on the catalyst particle is therefore an inherent requirement of the direct process of photocatalysis. In addition, the catalyst has to be located within an electrolyte in order that the material and charge balance may equalize. This electrolyte, which is also needed for versions b. and c. is shown by the prior art, however, to still lack satisfactory properties for mass and charge transfer.
b. Considered purely formally, a CO2 reduction catalyst and an H2O oxidation catalyst can be regarded as electrodes in an electrolytic system featuring a light-driven “voltage source”. Hereinbelow this is also defined as an electrically assisted photocatalysis. The CO2 reduction electrode and/or H2O oxidation electrode are photoelectrically active therein.
c. In a further simplification, the electrical energy for conducting the CO2 reduction and H2O oxidation comes from an external source of voltage. This source of voltage is more preferably driven using renewable sources of energy such as the wind or the Sun. A conventional electrolysis corresponds to this process.
Photochemical Reduction of CO2:
The prior art in photocatalysis is represented in table 1 and shows that the photochemical conversion of CO2 with water even under good lighting conditions only amounts to conversions in the region of μmol/g/h. This is perfectly understandable for thermodynamic reasons.
TABLE 1Conversion of CO2 with water under differentconditions and the resulting products as per the prior artLiteratureMainMaximumreferenceproductCatalystyieldLight sourceACS Appl. Mater.CH4WO3 Nano-~1.1 μmol/gh300 W Xe arcInterfaces 2012,sheetlamp4, 3372-3377J. Phys. Chem.CH4CdSe/Pt/TiO2~0.18 μmol/gh 300 W Xe arcLett. 2010, 1,lamp48-53Chem. Commun.,CH4Pt—MgO/TiO2~0.2 μmol/gh100 W Xe arc2013, 49,lamp2451-2453AppliedCH4Ag—TiO2~0.1 μmol/gh8 W Hg lampCatalysis B:Environmental 96(2010) 239-244Phys. Chem.COMgO~0.2 μmol/gh500 W ultrahighChem. Phys.,pressure mercury2001, 3,lamp1108-1113Chem. Eur. J.CH4TiO2/ZnO ~50 μmol/gh300 W Xe arc2011, 17,lamp9057-9061AppliedMeOHCu/TiO2 ~20 μmol/gh8 W mercury lampCatalysis B:Environmental 37(2002) 37-48AppliedCOI—TiO2~2.4 μmol/gh100 W Xe arcCatalysis A:lampGeneral 400(2011) 195-202Chem. Commun.,CH4Pt—ZnGeO4 ~28 μmol/ghfull arc Xe lamp2011, 47,2041-2043Angew. Chem.ReviewInt. Ed. 2013,article52, 2-39
If the reaction is carried out in air, then the accumulation of CO2 on the catalyst is a target to enhance the efficiency of the system. In addition to the accumulation of CO2, a certain proportion of water should also be present in the reaction environment in order to supply the corresponding amount of protons. The optimum ratio of H2O and CO2 can play an important part here. The main products formed vary according to the catalyst and are very frequently reported in the literature as CH4 and CO.
Electrochemical Reduction of CO2:
It was not until the 1970s that there were increasing attempts to systematically study the electrochemical reduction of CO2. Despite many strenuous efforts, no electrochemical system capable of reducing CO2 to competitive energy carriers in a sustainable and energetically favorable manner with sufficiently high current density and acceptable yield has hitherto been successfully developed. Owing to the increasing scarcity of fossil fuel resources and the volatility in the availability of renewable sources of energy, interest has come to be more and more focused on research in CO2 reduction.
The electrolysis of CO2 generally utilizes metal catalysts. Table 2 (derived from: Y. Hori, Electrochemical CO2 reduction on metal electrodes, in: C. Vayenas, et al. (Eds.), Modern Aspects of Electrochemistry, Springer, New York, 2008, pp. 89-189) shows the typical Faraday efficiencies over various metal electrodes. Over Ag, Au, Zn, Pd or Ga for instance CO2 is nearly exclusively converted into CO, whereas over copper a multiplicity of hydrocarbons are observed as reduction products.
TABLE 2Typical Faraday efficiencies for the conversionof CO2 over various electrode materialsElectrodeCH4C2H4C2H5OHC3H7OHCOHCOO−H2TotalCu33.325.55.73.01.39.420.5103.5Au0.00.00.00.087.10.710.298.0Ag0.00.00.00.081.50.812.494.6Zn0.00.00.00.079.46.19.995.4Pd2.90.00.00.028.32.826.260.2Ga0.00.00.00.023.20.079.0102.0Pb0.00.00.00.00.097.45.0102.4Hg0.00.00.00.00.099.50.099.5In0.00.00.00.02.194.93.3100.3Sn0.00.00.00.07.188.44.6100.1Cd1.30.00.00.013.978.49.4103.0Tl0.00.00.00.00.095.16.2101.3Ni1.80.10.00.00.01.488.992.4Fe0.00.00.00.00.00.094.894.8Pt0.00.00.00.00.00.195.795.8Ti0.00.00.00.00.00.099.799.7
The reaction equations which follow illustrate the reactions at the anode and at the cathode for the reduction over a silver cathode by way of example. The reductions over the other metals are similar.cathode: 2CO2+4e−+4H+→2CO+2H2Oanode: 2H2O→O2+4H++4e−
One of the primary issues with this electrolysis is that the electrolyte not only has to be very highly conductive, in order to have a low voltage drop, but also has to have a good CO2 solubility, in order to make sufficient CO2 available at the electrode for reduction. This is not possible in the previously discussed aqueous systems owing to the low solubility of CO2 in water (˜3 g of CO2 per 1 liter at 1 bar and 20° C.)
Specifically at high current densities, the scissioning reaction of water is dominant in these aqueous systems, since insufficient CO2 molecules are available at the cathode for reduction.
The use of ionic liquids to reduce CO2 has hitherto not been extensively described in the literature. The two publications hereinbelow utilize the known compound [EMIM]BF4 (formula depicted hereinbelow):                Reduction of CO2 to CO over silver electrode: B. A. Rosen, A. Salehi-Khojin, M. R. Thorson, W. Zhu, D. T. Whipple, P. J. A. Kenis, and R. I. Masel, Science 334, 643-644 (2011).        Reduction of CO2 to CO over bismuth electrode: J. L. DiMeglio, and Rosenthal Joel, Journal of the American Chemical Society 135, 8798-8801 (2013).        

1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4)
In addition, U.S. Pat. No. 5,788,666 also discloses the use of immobilized forms of proton traps for pH buffering.
WO 2010/093092 discloses the use of polymers having an amino group to precipitate calcium carbonate, but not in electrochemical applications.
There is a need for an electrolyte and a method of reacting carbon dioxide and water using an electrolyte having an improved efficiency of carbon dioxide conversion.